Certain operating conditions may cause the output hub for a torque converter in a vehicle to rotate faster than the turbine for the converter. For example, in coasting mode, engine braking mode, and regeneration mode for a hybrid vehicle, the hub rotates faster than the turbine. The hub and turbine are rotationally connected and the hub causes the turbine to rotate, which unfortunately, causes the torque converter to operate in what can be thought of as a “reverse” mode. In the coasting, engine braking, or regeneration modes, the drive unit for the vehicle is typically idling or even shut off, such that the drive unit is providing nominal torque to the pump. The rotation of the turbine reverses the typical fluid flow patterns in the converter and the turbine “pumps” fluid to the pump. This operation of the turbine is undesirable since the rotation of the turbine heats the oil in the turbine, resulting in excessive heat losses, and in some cases, even damage to the torque converter.
Also, in some modes, such as regeneration mode in a hybrid vehicle, it is desirable, if not necessary, to prevent rotation of the internal combustion engine. Unfortunately, although the “reverse” mode noted above is inefficient, rotating the turbine can transfer some torque to the pump and subsequently to the internal combustion engine. It is known to use clutches or gear arrangements in the transmission to disconnect the input shaft from the torque associated with the regeneration mode, however, such measures increase the cost and complexity of the transmission.
In some cases a direct “reverse” linkage between the vehicle transmission and the vehicle drive unit is desirable. For example, in an engine braking mode, the transmission is linked to the engine to use the inertia of the engine to slow down the transmission and wheels connected to the transmission. In a typical torque converter, the above linkage would be effected by the “reverse” mode noted above, with its attendant disadvantages, such as excessive heat losses.
Thus, there is a long-felt need for a means of controlling the rotational engagement of a turbine and an output hub in a torque converter. Specifically, there is a long-felt need for a means of enabling a transmission input shaft in a torque converter to receive torque downstream from the torque, converter without rotating the turbine in the converter or a means of rotationally disconnecting a turbine and a hub in a torque converter when the hub rotates faster than the turbine.